Rainbows

Before the scientific secrets
of rainbows were discovered,
these colorful bands of
light were wrapped in mystery
and folklore. Every culture
had its own theory for the
rainbow’s purpose,
and many times it had religious
significance. Rainbows have
been called such things
as the tongue of the sun,
road of the dead, bride
of the rain, hem f the sun-god’s
coat, road of the thunder
god, bridge between heaven
and earth, window to heaven,
and bow of God. Biblical
accounts establish the rainbow
as a covenant, or promise,
between God and every living
creature that the earth
never again will be destroyed
by flood.

Superstitious beliefs also
surround the rainbow. One
tribe in South America believed
a rainbow oer the sea was
a good sign, but when it
appeared over land, it was
the sign of an evil spirit
looking for a victim. In
Eastern Europe it was believed
that an angel put gold at
the ends of the rainbow,
but only a nude man could
find it. An old Romanian
folktale claimed that the
end of a rainbow stood in
a river, anyone creeping
in on hands and knees for
a drink of the rainbow-touched
water would be changed instantly
to the opposite sex. A similar
tale claimed that anyone
passing beneath a rainbow’s
arch would be changed into
the opposite sex.

Although rainbows are surrounded by folklore, superstition, and religious beliefs, they have a very common reason for existing. They result when sunlight is refracted and reflected by raindrops. In the primary rainbow, red lies on the outer edge of the arch and violet on the inner edge. A fainter, secondary rainbow sometimes can be seen outside the primary one. The light rays in the secondary rainbow strike the raindrops at a higher angle than those in the primary one and are reflected twice. This makes the resulting rainbow’s colors fainter and reverses the order. Red lies on the inner edge and violet on the outer edge of the secondary rainbow.

Rainbow colors also have
had their significance in
folklore. Some people believed
that when red was the most
brilliant, or noticeable,
it meant war; green meant
abundance; and yellow meant
death. Such superstitious
beliefs seem foolish to
us today, but these earlier
cultures, with their limited
scientific knowledge, had
no way of knowing the colorful
bands of light were produced
by sunlight being refracted
(bent) and reflected (turned
back) by raindrops.

In order to understand
how this happens, we must
learn a little about light.
Sunlight is a mixture of
color rays, and these rays
travel in wavy lines. The
distance between the tops
of the waves, which varies
in different rays from 14-
to 28-millionths of an inch,
is called the wave length.
Each different wave length
produces a different color.
Red and yellow wave lengths
are longer than those which
produce blue and violet
light, and the combination
of all colors produces white
light.

You can separate the colors
contained in sunlight by
using a simple prism, which
is a triangular bar of glass.
As light waves enter the
prism, they are refracted.
Since each color has a slightly
different wave length, each
is bent at a slightly different
angle. This separates them,
and they emerge from the
prism in bands of colors—red,
orange, yellow, green, blue,
indigo, and violet. These
seven bands of color are
called the solar spectrum.

When sunlight passes through
air filled with water droplets,
each of the raindrops acts
as a tiny prism to bend
and separate the light into
its many colors. But instead
of allowing the light to
pass through, as a prism
does, the inner surface
of the raindrop reflects
the color. Upon leaving
the raindrop the color is
bent again. The result of
this refraction and reflection
is a rainbow.

All of the colors of the
solar spectrum are present
in a rainbow, but since
they blend or overlap somewhat,
you rarely see more than
four or five colors clearly.
The color on the outer edge
of the arch is red, and
violet lies on the inner
edge. The width of the color
bands depends upon the size
of the raindrops forming
the rainbow.

Certain conditions must
exist before a rainbow can
be seen. The sun must be
behind you and low enough
on the horizon for its rays
to be reflected at the proper
angle to reach your eyes.
The rain must be somewhere
in front of you. Since sunshine
and rain showers appear
together most frequently
in the summer, more rainbows
are seen during this season.

Raindrops act as tiny prisms and mirrors that bend and separate sunlight into the seven colors of the spectrum and reflect these color rays back to our eyes as a rainbow. Each raindrop produces the entire spectrum, but we see only those color rays that reach our eyes at certain angles. In the primary rainbow, violet arrives at a forty-degree angle, red at forty-two degrees, and the remaining five colors at angles between the two. Since the colors blend and overlap somewhat, we rarely see more than four or five colors clearly. The width of the color bands depends upon the size of the raindrops forming the rainbow.

At this point, you may
be wondering how a rainbow
remains the same while the
raindrops are falling. Each
drop contributes to the
color for only a second,
but since each falling drop
is quickly replaced by another,
the reflected rays give
the appearance of never
changing. We do not see
all of the rays reflected
by the many raindrops present
in a shower. Those reflected
at forty- to forty-two-degree
angles form the primary
rainbow. Violet rays arrive
at our eyes at a forty-degree
angle, red at forty-two
degrees and the remaining
five colors at degrees between
these two.

A secondary rainbow, located
a short distance outside
the primary one, sometimes
can be seen. Its rays reach
the eye at fifty- to fifty-four-degree
angles. This secondary rainbow,
which some people incorrectly
think is a reflection of
the primary one, has a full
spectrum of colors; however,
the colors always are fainter
and the order reversed.
Red lies on the inner edge
of the secondary rainbow
and violet on the outer
edge. The light rays forming
the secondary rainbow strike
the raindrops from a higher
angle and are reflected
twice before leaving the
raindrop. This double reflection
accounts for the fainter
appearance and the reversed
order of color.

You may think you have
seen the complete rainbow
as it arched from one point
on the horizon to another,
but you really haven’t.
Rainbows can for a full
circle. If you were standing
on a high mountain and the
sun appeared low enough
on the horizon to create
a rainbow, you might see
a round round one. Passengers
in airplanes occasionally
do when conditions are right.

With the help of a harden
hose, you can make your
own rainbow. During the
early morning or late afternoon,
put the sun at your back
and spray a fine mist of
water into the air in front
of you. A circular rainbow
should be reflected by the
water droplets. Increase
the size of the water droplets
and notice whether the width
of the bands of color changes.
Mist from a plunging waterfall
will produce a similar rainbow
on a sunny day.

Proving the scientific
theory that sunlight is
a combination of colors
can be a fascinating experience.
Perhaps you already have
had a chance to experiment
with a simple prism in your
science class and have separated
sunlight into its various
colors, but have you ever
produced the solar spectrum
with a water prism? A water
prism is easy to make. All
you need is an oblong, blass
dish at least two inches
deep, a small mirror, a
piece of foil large enough
to wrap around the mirror,
a rock, and a large, white
card.

Fill the dish with water
and set it in the sunlight.
Cut a window one-inch tall
by one-half-inch wide in
the middle of the piece
of foil. Center the window
on the mirror and wrap the
foil around the edges to
hold the window in place.
Put the foil-covered mirror
in the water with the window
facing the sun. The top,
back edge of the mirror
should be leaning against
the side of the dish. Adjust
the angle of the mirror
until a color spectrum is
reflected on a nearby wall.
Use the rock to keep the
mirror from slipping once
you have it at the proper
angle. Insert the white
card between the dish and
the wall image and the spectrum
should appear on the card.
The water refracts the light,
separating it into its colors,
and the mirror reflects
these colors onto the card.

To bring the colors back
together, place a magnifying
glass in the path of the
reflected light, holding
it several inches from the
card and facing the mirror.
A rectangle of white light
the shape of the foil window
should now be projected
on the white card instead
of a color spectrum. By
adjusting the angle of the
magnifying glass, you should
get a sharp outline of the
window. The curved lens
of the magnifying glass
has brought the color rays
back together, producing
white light, but you have
proved with your water prism
that sunlight is a combination
of colors.

Up to now, all of the rainbows
mentioned have been caused
by reflected sunlight, but
a study of rainbows would
not be complete without
mentioning that moonlight
occasionally is responsible
for rainbows. The feebleness
of moonlight results in
very faint colors, making
a lunar rainbow very difficult
to see; however, the lunar
rainbow differs from those
made by the sun only in
the intensity of its color.
All rainbows, whether produced
by sunlight or moonlight,
are a result of light being
refracted and reflected
in moisture.